In the marketplace for ready-to-eat cereals or snacks, products with a light, crisp texture have become very popular. This is especially true with respect to ready-to-eat cereals based on crisp rice and snack products based on crisp corn. The ready to eat cereals have excellent crispness retention in milk, excellent organoleptic characteristics, and a low density that makes possible the use of large, appealing packages. It is possible that an oat based cereal or snack product of this type could also find consumer acceptance.
Manufacture of crisp, light cereal products is typically undertaken by expanding whole grains or cereal flour mixtures using two principal methods. First, a sudden release of pressure on a cooked whole grain or cooked cereal flour can cause substantial expansion by allowing entrapped gases and superheated liquids within the cereal to expand rapidly. Gun puffing and extrusion puffing in which the cereal is first subjected to superatmospheric pressure and then released to atmospheric or subatmospheric pressure are typical methods of expansion by release of pressure. Second, application of heat to cooked whole grain or cooked cereal flour mixtures can also result in substantial expansion by sudden vaporization of liquids and expansion of gases entrapped within the cereal. Typical methods for expansion of cereals by heating include immersion of the cereal in hot oil or introduction of the cereal into a hot airstream.
Many cereals are easily expanded. For example, if corn, wheat, or rice flours are expanded by extrusion from a cooker-extruder and are cut and then dried, a crisp, porous product with a stable low density structure is produced. A typical shape for such highly expanded cereals is an irregular nugget shape about 3/16 to 5/16 inch in diameter. Typical densities for these products when extruded under heat and pressure at a 20% moisture content are in the range of 4 to 8 ounces in a box volume of 121.5 cubic inches. Maximum expansion of these corn, wheat and rice cereals typically requires a low moisture content, generally in the 12 to 20% range, combined with a high temperature of extrusion, generally well above 300.degree. F.
Until now, problems in making a highly expanded crisp oat product have prevented its commercial production. For example, oat flour processed at the 20% moisture conditions described above produces a product which is hard and substantially unexpanded with a density of about 15-20 ounces for a box volume of 121.5 cubic inches. It has been observed that low moisture oat flour mixtures expand normally as they issue from an extrusion die but undergo a sudden collapse immediately following extrusion.
This amount of expansion makes an unacceptable product from a consumer and marketing viewpoint. It has been determined that consumers prefer a light, crisp product with a substantially lower density. Although product densities in the range of 4 to 8 ounces per 121.5 cubic inches are preferred by consumers, cereal products with a density as high as about 12 ounces per 121.5 cubic inches could also find consumer acceptance.
As a result of the difficulties of oat flour expansion, the only types of low density oat flour cereal products currently available are hollow pillow or biscuit shapes as described, for example, in U.S. Pat. No. 3,054,677 issued to Graham et al. Graham describes a method for making a pillow shaped cereal in which an oat flour mix is extruded under heat and pressure into adjacent strands which expand as they issue from the die, thereby contacting and bonding to each other, and then pinching off sections of the bonded strands to form hollow, pillow shaped pieces, followed by heating the pieces to blister and set the strands. No oat cereal has a highly expanded, porous structure in which small, randomly distributed voids throughout the cereal provide the reduced bulk for a low density cereal product.
Efforts have, of course, been made to remedy this situation. A notable effort was made by Rupp, as described in U.S. Pat. No. 2,552,291, in which he taught the use of solvent extraction on dehulled oat and milled oat products to remove the oat lipids which inhibited expansion of oats and oat products. His tests indicated that substantial improvement in expansion of oats and oat products can be produced in a variety of expansion methods (in at least one test, expansion was doubled) from solvent extracted defatted oats and oat products.
Although Rupp was successful in his efforts to produce an oat cereal product with substantially improved expansion, it would also be desirable to make a highly expanded cereal by using a simple method that does not require extraction of oat lipids.
It is therefore an object of the present invention to provide a method of making light, crisp oat flour based cereal products having a highly expanded, porous structure, by a method which does not require extraction by solvents to remove oat lipids, such that the oat cereal product has a density, when measured as irregular nuggets about 3/16 to 5/16 inches in diameter, of less than about 12 ounces in a box volume of 121.5 cubic inches.
It is also an object of the present invention to provide a method for improving the expansion of expanded cereal products containing oat flour by a method which does not require extraction by solvents to remove oat lipids.